i allways find pistons for sohc zc's and i was wondering if you can use sohc pistons in a dohc motor

depends which DOHC motor u'r refering to. sumone correct me if i'm wrong, but i'm pretty sure all D-series motors have the same bore 75mm (SOHC and DOHC). so the only thing u'd have to worry about would be piston-to-valve clearances.

the pistons are for a zc

I think that it will only work in a DOHC ZC.
Both motors came with the domed pistons
and a large pent combustion chamber to handle the pistons.

Otherwise there are valve clearance issues.

They Will not work in any DOHC b-motors

well those motors had high compression to begin w/ so u'd be pretty safe w/ any stock sized SOHC piston because they were all lower compression than the DOHC ZC. however, if u go w/ too low of a compression piston, u'r gonna "feel" it. if u'r lookin for aftermarket, just don't go too high of a dome or too tall of a piston or u'll smack the crap out of u'r valves or, if the compression is too high and u run pump gas, blow the motor.